02/21/2012
Model Study Investigates Roles of Ocean and Atmospheric Processes in Reducing Arctic Ice Edges
Summary
The polar ice edge, or marginal ice zone (MIZ), is a key area since it is erodes first; however, it is not known how much of the erosion results from atmospheric heating or from oceanic advection of warm waters. This DOE-funded model study uses the DOE-supported POP ocean and CICE sea-ice models to investigate and compare these processes. The model passes an important test of sea-ice distribution changes: when the model is driven by the observed-reanalysis winds of the 1990s, it successfully simulates the observed dipole pattern of ice concentration changes characteristic of the changes associated with North Atlantic Oscillation (NAO) pressure and circulation changes. The model successfully simulates the first mode of sea ice concentration variability, which is characterized by a dipole pattern of ice concentration anomalies, coherent with the atmospheric NAO pressure pattern. The model ocean-ice system was forced with NCEP/NCAR atmospheric reanalysis and then run for the two NAO periods during the 1990s. The upper ocean mixed layer heat budgets were analyzed in the Barents, Nordic, and Irminger seas to determine the winter-to-winter changes in the ocean heat advection and mixed layer net fluxes, and these were then related to the ice changes. The researchers found that bottom ice melt dominates the top ice melt, signifying the role of the ice-ocean heat exchange for the ice thermodynamics. The ocean advection anomalies were also closely related to anomalous bottom ice melt rates. However, although the oceanic temperature advection is of the same order of magnitude as the net atmospheric heat fluxes, the latter are always larger. Entrainment of heat from the deeper ocean may also play a key role in the upper ocean heat balance, which may be strongly influenced by ocean heat advection. Future research will consider the role of the deeper ocean upwelling and continue to investigate the relative importance of atmospheric and oceanic processes in eroding polar sea-ice.
References
Ivanova, D. P., J. L. McClean, and E. C. Hunke. 2012. “Interaction of Ocean Temperature Advection, Surface Heat Fluxes, and Sea Ice in the Marginal Ice Zone During the North Atlantic Oscillation in the 1990s: A Modeling Study,” Journal of Geophysical Research 117, C02031. DOI: 10.1029/2011JC007532.